I've witnessed coyotes chasing squirrels in the woods. And using a stick I've dissected coyote poop and seen it filled with those little squirrel claws. In my neck of the Ozark's it is nearly all heavy timber and squirrel populations are usually pretty good. Some years on an upswing in the population the numbers of squirrels can be danged near scary - they are running around everywhere in extremely high numbers. I've sat on a deer stand where visibility was no more than 100 yards because of terrain and timber and counted as many as two dozen squirrels within view, move a 1/4 mile and see that many again. I've done this nearly all day long some days - that's a lot of squirrels. No doubt they provide protein and plenty of it to coyotes, bobcats, owls, hawks, ect. I've actually seen coyotes chasing squirrels, seen bobcat tracks in the snow where they've caught and killed squirrels, and watched both owls and hawks catch squirrels in the woods. I think in my neck of the woods squirrels replaces the cottontail rabbit we think of most often as prime prey in many other areas because of availability. In fact, I often use a squirrel distress for a stand alone distress call and do quite well with it.